1. Field
Embodiments of the invention relate to electronic devices, and more particularly, to amplifiers.
2. Description of the Related Technology
A voltage feedback amplifier can refer to an amplifier connected in a closed-loop configuration in which the error signal is a voltage signal. In contrast, a current feedback amplifier can refer to an amplifier connected in a closed-loop configuration in which the error signal is a current signal.
FIG. 1 is a circuit diagram of a prior art current feedback amplifier 30. The current feedback amplifier 30 includes a non-inverting input terminal IN+, an inverting input terminal IN−, an output terminal OUT, a first stage 1, a second stage 2, a third stage 3, a compensation capacitor 4, and a feedback circuit 5. The first stage 1 includes first and second input NPN bipolar transistors 11, 12, first and second input PNP bipolar transistors 13, 14, and first and second current sources 15, 16. The second stage 2 includes first and second current mirror NPN bipolar transistors 21, 22 and first and second current mirror PNP bipolar transistors 23, 24. The feedback circuit 5 includes first and second feedback resistors 6, 7.
The input stage 1 can be used to generate a first output current IOUT1 and a second output current IOUT2, which can change in response to a current feedback signal 9 and a differential input signal received between the non-inverting and inverting input terminals IN+, IN−. The second stage 2 can be used to mirror the first and second output currents TOUT1, IOUT2 to generate first and second mirrored currents IM1, IM1, which can be used to charge or discharge the compensation capacitor 4. The output stage 3 can be configured to operate as a voltage buffer, and can be used to control a voltage level of the output terminal OUT based on the voltage across the compensation capacitor 4. The first and second feedback resistors 6, 7 can generate the current feedback signal 9, which can be used to adjust the magnitude of the first and/or second output currents IOUT1, IOUT2 so as to charge or discharge the compensation capacitor 4 and control the amplifier's output terminal OUT to a voltage level associated with the first and second output currents IOUT1, IOUT2 being balanced or equalized.
Current feedback amplifiers, such as the current feedback amplifier 30 of FIG. 1, can have faster output slew rates and/or larger bandwidth relative to certain voltage feedback amplifiers. However, current feedback amplifiers can also have relatively worse DC performance characteristics, such as a relatively large input offset voltage, a relatively high input bias current, and/or a relatively poor common-mode rejection ratio (CMRR).
Accordingly, there is a need for improved amplifiers, including, for example, amplifiers having increased bandwidth, improved CMRR, and/or reduced input offset error.